1. Field of the Invention
The present invention relates to a package of a semiconductor device, more particularly to a structure of a package having pins which electrically connect to a circuit board, under a contacting condition.
2. Description of the Prior Art
In recent years, leadless packages, also known as chip carriers, have come into increasing use of accommodating integrated circuits (IC), large-scale integrated circuits (LSI), and the like. Like conventional packages with outer leads, leadless packages accommodate an IC chip therein and outer pads of the leadless package are electrically connected to the substrate and circuit board by soldering. They therefore can be used in popular assembly processes. At the same time, provision of conductor pads as outer pads in place of outer leads enables a more compact structure. Therefore, such packages can be mounted at a higher density on a circuit board, etc. compared with other packages. This highly prized feature has resulted in leadless packages being widely used in a broad range of fields.
There is, however, a problem with mounting the package to the substrate and circuit board by a rigid soldering technique in that the electrical connections tend to fracture during a heat procedure. Normally, the package, substrate, and circuit board are formed of different materials having different coefficients of expansion. During the heating required to accomplish the mounting and during normal operating conditions, the package, substrate, and the circuit board contract and expand at different rates, thereby generating stresses. These stresses can fracture the package, substrate, circuit board, or soldered conductor pads. The problem is compounded the greater the size of the devices on the circuit board. Such breakage, of course, has a fatal effect on the operation of the electronic circuits formed on the circuit board.